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<table width="100%" summary="page for mecter"><tr><td>mecter</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Mechlorprop and terbythylazine tested on Lemna minor</h2>

<h3>Description</h3>

<p>Data consist of 5 mixture, 6 dilutions, three replicates, and 12 common controls; in total 102 onservations.
</p>


<h3>Usage</h3>

<pre>data(mecter)</pre>


<h3>Format</h3>

<p>A data frame with 102 observations on the following 3 variables.
</p>

<dl>
<dt><code>dose</code></dt><dd><p>a numeric vector of dose values</p>
</dd>
<dt><code>pct</code></dt><dd><p>a numeric vector denoting the grouping according to the mixtures percentages</p>
</dd>
<dt><code>rgr</code></dt><dd><p>a numeric vector of response values (relative growth rates)</p>
</dd>
</dl>



<h3>Details</h3>

<p>The dataset is analysed in Soerensen et al (2007). 
The asymmetric Voelund model is appropriate, whereas the symmetric Hewlett model is not.
</p>


<h3>Source</h3>

<p>The dataset is kindly provided by Nina Cedergreen, Department of Agricultural Sciences, 
Royal Veterinary and Agricultural University, Denmark.
</p>


<h3>References</h3>

<p>Soerensen, H. and Cedergreen, N. and Skovgaard, I. M. and Streibig, J. C. (2007) 
An isobole-based statistical model and test for synergism/antagonism in binary mixture toxicity experiments, 
<em>Environmental and Ecological Statistics</em>, <b>14</b>, 383&ndash;397.
</p>


<h3>Examples</h3>

<pre>

## Fitting the model with freely varying ED50 values
mecter.free &lt;- drm(rgr ~ dose, pct, data = mecter, 
fct = LL.4(), pmodels = list(~1, ~1, ~1, ~factor(pct) - 1)) 

## Lack-of-fit test
modelFit(mecter.free)  # not really acceptable
summary(mecter.free)

## Plotting isobole structure
isobole(mecter.free, exchange = 0.02)

## Fitting the concentration addition model
mecter.ca &lt;- mixture(mecter.free, model = "CA")

## Comparing to model with freely varying e parameter
anova(mecter.ca, mecter.free)  # rejected

## Plotting isobole based on concentration addition
isobole(mecter.free, mecter.ca, exchange = 0.02)  # poor fit

## Fitting the Hewlett model
mecter.hew &lt;- mixture(mecter.free, model = "Hewlett")

## Comparing to model with freely varying e parameter
anova(mecter.hew, mecter.free)  # rejected

## Plotting isobole based on the Hewlett model
isobole(mecter.free, mecter.hew, exchange = 0.02)  # poor fit

## Fitting the Voelund model
mecter.voe&lt;-mixture(mecter.free, model = "Voelund")

## Comparing to model with freely varying e parameter
anova(mecter.voe, mecter.free)  # accepted

## Plotting isobole based on the Voelund model
isobole(mecter.free, mecter.voe, exchange = 0.02)  # good fit

</pre>


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